This invention relates to an apparatus and method for processing (e.g. etching, chemical or physical vapor deposition, etc.) a substrate in a chamber containing a plasma. More specifically, this invention provides an apparatus and method for plasma processing of a semiconductor wafer. This invention allows a generally stable processing power (e.g. radio frequency (RF) processing power) to pass through a dielectric member and into a chamber of a plasma processing apparatus such that an essentially stable and uniform processing (e.g. etch rate) on semiconductor wafers may be maintained over a desired period of time. 2. Description of the Prior Art
It is well known that various magnetically enhanced radio frequency (RF) diodes and triodes have been developed to improve performance of plasma reactors. As mentioned in an article entitled "Design of High-Density Plasma Sources" by Lieberman et al from Volume 18 of "Physics of Thin Films", copyright 1994 by Academic Press Inc. of San Diego, Calif., these include by way of example only, the Applied Materials AMT-5000 magnetically enhanced reactive ion etcher and the Microelectronics Center of North Carolina's split cathode RF magnetron. Magnetically enhanced reaction ion etchers (MERIE) apply a dc magnetic field of 50-100 Gauss (G) parallel to the powered electrode which supports a semiconductor wafer. The dc magnetic field enhances plasma confinement, resulting in a reduced sheath voltage and an increased plasma density when the magnetic field is applied. However, the plasma generated in MERIE systems is strongly nonuniform both radially and azimuthally. It is well known that in order to increase process uniformity, at least azimuthally, the magnetic field is rotated in the plane of the semiconductor wafer at a certain frequency, e.g. 0.5 Hz. While this is an improvement, MERIE systems still do not have the desired uniformity and high density in the generated plasma, which may limit the applicability of MERIE systems to next-generation, sub-micron device fabrication.
The limitations of RF diodes and triodes and their magnetically enhanced variants have led to the development of reactors operating at low pressures with high-efficiency plasma sources. These reactors can generate a higher density plasma and have a common feature in that processing power (e.g. RF power and/or microwave power) is coupled to the plasma across a dielectric window, rather than by direct connection to an electrode in the plasma, such as for an RF diode. Another common feature of these reactors is that the electrode upon which the wafer is placed can be independently driven by a capacitively coupled RF source. Therefore, independent control of the ion/radical fluxes through the source power and the ion bombarding energy through the wafer electrode power is possible.
While the limitations of RF diodes and triodes and their magnetically enhanced variants have motivated the development of high-density plasma reactors with low pressures, high fluxes, and controllable ion energies, these developed high-density plasma reactors have a number of challenges. One challenge is the inability of high-density plasma reactors to achieve the required process uniformity over 200-300 mm wafer diameters. High density sources are typically cylindrical systems with length-to-diameter usually exceeding unity. In such cylindrical systems plasma formation and transport is inherently radially nonuniform.
Another challenge is that the deposition of materials on the dielectric window during etching of semiconductor wafers in a process chamber has necessitated frequent and costly reactor cleaning cycles. This is especially true when metals, such as platinum, copper, aluminum, titanium etc., are etched or deposited in the production of integrated circuit (IC) devices. After a metal layer on a substrate has been etched or deposited for a period of time, the etch or deposit rate on the metal may decrease. The dropping in metal etch or deposit rate is due to the build up of conductive by-products deposited on the dielectric window. Such deposited conductive by-products behave as a Faraday shield to reduce the efficiency of rf energy transmission into the plasma by blocking the rf energy transmission through the dielectric window. Thus, there is no stable power transmission into the plasma processing chamber; and there is no efficient power transfer across dielectric windows over a wide operating range of plasma parameters.
Therefore, what is needed and what has been invented is a method for adjusting the density of plasma in a plasma processing chamber in proximity to a certain situs on a surface (i.e. an inside or outside surface) of the dielectric window. What is further needed and what has been invented is an assembly for allowing stable power transmission into a plasma processing chamber over a long period of time during processing of a substrate (i.e. semiconductor wafer) contained within the plasma processing chamber. The substrate supports a metal layer which is etched or deposited when processing power (e.g. RF power) is passed through a dielectric window and into a processing chamber containing the substrate and a plasma of the processing gas.